Device for optical communication between electronic modules

ABSTRACT

The device enables bi-directional optical communication between a master module and slave modules by means of an optical rod ( 1 ) made of transparent material. The master module is axially coupled to the rod. The modules are arranged laterally along a useful part of the rod bounded by a lateral reflector located opposite the slave modules. The lateral reflector can be formed by a plurality of adjacent notches ( 12 ) formed at the surface of the rod and constituting a continuous reflecting zone in the form of serrated teeth, and/or by a narrow reflecting strip ( 17 ). The slave modules can be positioned anywhere along the useful part of the rod and their lateral location is not critical, a lateral coupling zone extending over at least 1 cm outside the rod. Such a device can be advantageously used in an electrical panel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application based onPCT/FR02/01165, filed Apr. 4, 2002, the content of which is incorporatedherein by reference, and claims the right to priority based on foreignapplication FR 01/07565 filed Jun. 11, 2001, the content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a device for optical communication betweenelectronic modules comprising an optically conducting rod, having firstand second ends, designed to be optically coupled, by lateral coupling,to lateral electronic modules arranged laterally along the rod, andcomprising lateral reflecting means arranged over a longitudinal part ofthe external surface of the rod opposite the lateral modules.

A large number of devices exist enabling optical interconnection ofelectronic modules.

In a first type of device, as described in the document EP-A-587,066 forexample, an optical communication bus is formed by a plurality ofmodular electrical equipment units arranged side by side. Each unit isequipped on one side face with an opto-electronic receiver and on theopposite side face with an electro-optical transmitter electricallyconnected to the receiver. Each unit can thus communicate optically withthe adjacent units. This type of device presents a major drawback inthat, if one of the units fails, the communication chain is broken.

Backplane optical busses also exist, generally constituted by a platemade of glass or transparent plastic material comprising means foroptical coupling with printed circuit boards, each board comprising atleast one electro-optical transmitter and one opto-electronic receiver.Various coupling means, arranged on the face of the bus adjacent to theprinted circuit boards, have been described, in particular windows madeof a light-absorbing material (WO-A-8,503,179), grooves (GB-A-2,208,566)and diffraction networks (U.S. Pat. No. 5,091,985). U.S. Pat. No.4,744,617 describes an optical bus of circular, square or polygonalcross-section, comprising as coupling elements inclined reflectingsurfaces formed in the face of the bus opposite the printed circuitboards. In these different devices, the coupling elements are punctualand are fitted at predefined locations, associated to each of theprinted circuit boards. The number of printed circuit boards and theirlocations are thus predefined.

In the document EP-A-249,746, a multimode optical fiber comprising adiffusing core enables optical communication between transmitter andreceiver stations that are coupled laterally thereto. The stations canbe arranged at any location along the optical fiber. In this device,optical lenses fitted between the fiber and each of the stations have tobe placed in the immediate proximity of the fiber. The radialpositioning of the lenses and of the associated stations is relativelycritical.

In the document WO-A-9,839,861 a bi-directional optical transmissionsystem between electronic components uses light diffused in the airinside a channel bounded by the optically reflecting internal surface ofa U-shaped enclosure made of metal or plastic. The opto-electronictransmitter and receiver elements of the electronic components can bearranged at any location along the channel, but must on the other handadvance inside the channel. The distance of these components to thechannel is therefore precisely defined.

OBJECT OF THE INVENTION

The object of the invention is to achieve an optical communicationdevice not presenting the drawbacks of the prior art devices. Such adevice must in particular enable optical coupling of electronic moduleswithout requiring any special connectors or precise positioning of themodules.

According to the invention, this object is achieved by the fact that thelateral modules are slave modules designed to communicate with a mastermodule optically coupled, axially, to the first end of the rod, the rodcomprising a useful part equipped with lateral reflecting means forminga substantially continuous reflecting zone, the rod, which has across-section the surface whereof is greater than 15 mm², and thelateral reflecting means defining a continuous longitudinal lateralcoupling zone along the useful part of the rod so as to enablebi-directional optical coupling of the master module with a lateralmodule arranged at any location along the useful part of the rod, thelateral coupling zone extending over at least one centimeter outside therod.

According to a first development of the invention, the lateralreflecting means are formed by a plurality of adjacent notchesconstituting a reflecting zone in the form of serrated teeth along theuseful part of the rod.

According to a second development of the invention, the lateralreflecting means comprise a narrow reflecting strip.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention, givenas non-restrictive examples only and represented in the accompanyingdrawings, in which:

FIG. 1 is a schematic representation of a device according to theinvention,

FIG. 2 represents an electronic module of a device according to theinvention in greater detail,

FIG. 3 illustrates an optical fiber rod and the lateral coupling zone ofa device according to the invention,

FIGS. 4 to 12 represent various embodiments of a lateral reflector of adevice according to the invention,

FIGS. 13 to 16 represent different embodiments of the cross-section ofan optical fiber rod of a device according to the invention,

FIG. 17 represents a particular embodiment of coupling of the opticalfiber rod to a master module of a device according to the invention ingreater detail,

FIG. 18 illustrates the arrangement of a device according to theinvention in an electrical panel,

FIG. 19 illustrates an alternative embodiment of a device according toFIG. 18,

FIG. 20 illustrates a particular embodiment of a device according to theinvention.

DESCRIPTION OF PARTICULAR EMBODIMENTS

The optical communication device represented in FIG. 1 comprises anoptical fiber rod 1 forming a bi-directional optical communication busbetween a master electronic module 2 and n slave electronic modules 3 (3₁, 3 ₂, . . . , 3 _(n)). Each electronic module comprises, like themaster module 2 represented in FIG. 2, an electro-optical transmitter 4(laser diode, light-emitting diode, . . . ) and an opto-electronicreceiver 5 (photodiode, phototransistor) electrically coupled to anelectronic processing unit 6, preferably a microprocessor. The lattercan be electrically coupled for example by a bus 7 to external modules,supervisors, sensors, or actuators.

The optical fiber rod 1 is made from an optically conducting,electrically insulating material, such as glass, silica or preferablyplastic, the latter material presenting the advantage of being able tobe easily molded. Various thermoplastic materials can be used such aspolycarbonate, PMMA (polymethyl methacrylate), PVC, plexiglass, etc.

The optical fiber rod 1 has a cross-section greater than 15 mm²,preferably comprised between 25 and 100 mm2, much larger than thecross-section of conventional optical fibers. In a preferred embodiment,it is rigid and has a length of about 50 cm to 1 m.

Optical communication can be achieved by means of such a rod over shortdistances between the master module 2 and slave modules 3. The mastermodule 2 is optically coupled axially to a first end of the rod (on theleft in FIGS. 1, 3 to 12, 17 to 19). The lateral modules 3 are arrangedside by side laterally along the rod and communicate optically with theoptical rod 1 in a lateral coupling zone 8 represented in FIGS. 3 and19. The lateral coupling zone 8 is situated opposite a lateralreflector. It extends outside the rod over at least one centimeter,typically several centimeters for example, perpendicularly to thelongitudinal axis S of the optical rod 1. The lateral reflector 9 formsa substantially continuous reflecting zone over a longitudinal part ofthe external surface of the rod opposite the lateral modules 3. Thewidth of the reflecting zone is preferably limited to less than 25% ofthe perimeter of the cross-section of the optical rod (FIGS. 10 to 16and 20) to limit losses.

In a preferred embodiment, the optical rod 1 comprises at its first endan end section 10 not equipped with a lateral reflector 9. The lateralmodules 3 can not be arranged along the end section 10, but only alongthe useful part of the rod 1 facing the lateral reflector 9. An endreflector 11 (FIGS. 3, 4, 10 to 12, 18 and 19) is preferably arranged ona second end of the optical rod opposite the first end.

In a preferred embodiment, represented in FIG. 4, the optical rod 1 isof beveled shape, its cross-section decreasing substantiallycontinuously from the first end to the second end so as to limit thelosses in the optical rod and to optimize the efficiency of the device.For example purposes, the cross-section of the optical rod can varybetween 100 mm² at the first end and 50 mm² at the second end.Furthermore, the second preferably reflecting end 11 is inclined so asto send the light waves back in the direction of the lateral reflector9. To give an example, the angle α between the longitudinal axis S ofthe rod 1 and the second end can be comprised between 70° and 90°. In apreferred embodiment α=80°.

Different embodiments of the lateral reflector 9 are illustrated inFIGS. 4 to 12. The essential function of the lateral reflector is topartially transform, with minimum losses, the substantially radialpropagation of the light waves coming from a slave module 3 intosubstantially axial propagation and the substantially axial propagationof the light waves coming from the master module 2 into substantiallyradial propagation able to be detected by the slave modules 3. Thesurfaces not used for this function must enhance guiding of the lightwaves internal to the optical rod 1.

According to a first embodiment of the lateral reflector 9, the latteris formed by a plurality of adjacent notches 12, of depth h,constituting a substantially continuous reflecting zone, in the form ofserrated teeth with a pitch p, along the useful part of the rod. Eachnotch can be asymmetric (FIGS. 4 and 6 to 8) or symmetric (FIG. 5).According to a preferred alternative embodiment, represented in FIG. 6,two adjacent notches 12 are separated by an external flat surface 13 ofwidth 1 ₁.

When the notches 12 are asymmetric, they are each bounded by a firstoblique face 14 forming an angle β₁ with an axis perpendicular to thelongitudinal axis S of the optical rod, and a second oblique face 15,closer to the second end of the optical rod and forming an angle β₂,smaller than β₁, with the axis perpendicular to the longitudinal axis S.

To improve and homogenize the extraction efficiency of the light wavesalong the optical rod 1, it is possible to modify the pitch p, whichdecreases progressively between the first and second end of the opticalrod. According to an alternative embodiment (FIG. 7), an internal flatsurface 16 of variable width 1 ₂, decreasing progressively between thefirst and second ends, is provided in the bottom of the notches 12,between the oblique faces 14 and 15. In FIG. 7, the internal flatsurface 16 is reduced to zero at the second end of the optical rod.According to another alternative embodiment (FIG. 8), modification ofthe pitch p is obtained by modification of the angle β₁, which decreasesprogressively between the first and second ends of the rod. These twovariants can also be associated.

When the pitch is variable, according to the embodiment of FIG. 8, theangle β₁ can vary from 90°—the case where there is no light waveextraction close to the first end—to 45° at the second end of theoptical rod.

As an example, the dimensions of the lateral reflector can be asfollows:p=2 mmh=1 mm1₁=0.5 mmβ₁=45°β₂=27°

To increase the extraction efficiency, by about 10 to 15%, an additionallateral reflector 17 can be arranged parallel to the reflecting zoneformed by the notches so as to send the light rays diverted to theoutside on the side where the lateral reflector 9 is located back to theoptical rod 1. The additional lateral reflector 17 is formed by a narrowreflecting strip located in the immediate proximity of the reflector 9,either at a small distance (1 to 2 mm for example) as in FIG. 4, ordirectly in contact with the external flat surfaces 13, as in FIG. 9.

The additional lateral reflector 17 can be fixed by any suitable means.According to a particular embodiment, it can form an integral part of awhite reflecting plastic part having the additional function of holdingand protecting the optical rod 1. If it is in contact with the externalflat surfaces 13 (FIG. 9), it can be fixed by sticking or formed bymolding from a casting on the optical rod.

According to alternative embodiments of the invention represented inFIGS. 10 to 12, the lateral reflector 9 can be formed solely by a narrowreflecting strip formed on the useful part of the rod, although theperformances are then substantially lower than those of a device withnotches according to FIGS. 4 to 9. In this case, as in the case of theadditional lateral reflector 17 (FIGS. 4 and 9), several embodiments canbe envisioned. In FIG. 10, the reflecting strip is a continuousrectangular strip 18. According to an alternative embodiment representedin FIG. 11, the reflecting strip is a continuous strip 19 of variablewidth, minimal near to the first end of the rod, then increasing up to amaximum and thence decreasing. This enables the useful surface of thelateral reflector at its ends to be minimized. According to anotheralternative embodiment represented in FIG. 12, the reflecting strip isfragmented into elemental reflecting zones, thus forming a discontinuousstrip 20. The reflecting zones that constitute the latter have avariable length and/or surface, minimal near to the first end of the rodand increasing continuously in the direction of the second end. Thecharacteristics of the reflecting strips 19 and 20 can be combined.

The reflecting strip (18, 19, 20) can be formed by any suitable means onthe optical rod, for example by molding from a casting, by deposition ofa paint or by sticking. It can also be formed by micro-mirrors or by areflecting film behaving as a set of micro-mirrors.

The cross-section of the optical rod 1 can be rectangular (FIG. 13), thelateral reflector 9 being arranged on a first lateral face of the rodand the slave modules 3 arranged along the rod, facing a lateral faceopposite the first face. The cross-section is preferably circular (FIG.14) or ovoid (FIGS. 16 and 20), the lateral reflector being in this caselocated on a flattened face of the rod.

The optical rod 1 is preferably formed, at the same time as the notches12, by injection molding of a plastic material transparent at thetransmission wavelength of the electro-optical transmitters 4 of theelectronic modules 2 and 3 and presenting good temperature resistanceproperties. As a variant, it can also be manufactured by thermoformingor by extruding. The notches 12 can also be obtained by subsequentmachining of the optical rod.

The wavelength used can be chosen in the visible (in the green forexample) or preferably in the infrared for which high-integrationtransmitters and receivers are currently available. Integratedopto-electronic transmitter-receiver components for data transmission ofthe type referred to as “IRDA” can fulfill this function. The dataexchange protocol, of any known type, is managed by the master module 2.According to a preferred embodiment, the latter periodically transmits aframe initializing the exchanges. On receipt of this frame, each slavemodule 3 transmits in a time window allocated to it, scanning beingterminated after the last slave module 3 n has transmitted. The absence,or malfunctioning, of a slave module is detected by its silence in theallocated time window.

FIG. 17 illustrates a particular embodiment of connection of the opticalrod 1 to the master module 2. The rod 1 comprises at its first end twogrooves 21 designed for flush-mounted housing of diodes respectivelyconstituting the electro-optical 4 transmitter (light-emitting diode)and the opto-electronic receiver 5 (photodiode) of the master module 2.

An application of a device according to the invention in an electricalpanel 22 is illustrated in FIG. 18. A plurality of modular electricalcontrol/monitoring and/or protection units, for example circuitbreakers, switches and/or relays, constituting the slave modules 3 ₁, 3₂, . . . , 3 _(n), are arranged side by side in the panel, along anoptical rod 1 fixed by any suitable means in the panel. In order tomaximize the number of slave modules able to communicate by means of theoptical rod 1, the master module 2, constituted by a control/monitoringmodule, is preferably arranged at a location remote from the panel. InFIG. 18 the rod 1 is horizontal, and the master module 2 is locatedremotely in the vertical and upward direction. Axial optical connectionthereof with the first end of the rod 1 is performed by means of anadditional optical rod 23 arranged perpendicularly to the rod(vertically in FIG. 18) and comprising, at its bottom part in FIG. 18, acoupling end for coupling with the first end of the rod 1. The couplingend of the additional optical rod 23 comprises an external face incontact with the first end of the rod 1 and a reflecting end surface 24forming an angle of 45° with the first end of the rod.

According to an alternative embodiment illustrated in FIG. 19, the rod 1is bent at its first end so as to comprise an end part perpendicular tothe useful part of the rod, enabling the master module 2 to be locatedremotely.

According to the particular embodiment of a device according to theinvention illustrated in FIG. 20, the optical rod 1, of ovoidcross-section, is housed at the bottom of a rail 25, of DIN type forexample, designed to act as support for slave modules 3. The slavemodules 3 are conventionally arranged side by side on the rail. Theyeach comprise a transmitter element 4 and receiver element 5 at theirbottom part facing the inside of the rail. They can thus communicatewith a master module by means of the optical bus formed by the rod. Suchan arrangement enables existing panels not provided with this opticalcommunication function to be completed, without any special adaptationbeing required for fitting the rod.

As an example, in a device of this type, 16 slave modules with a widthof 35 mm can communicate with a master module by means of an optical rod1 having a useful length of 56 cm, with signals of about 100 milliwatts(mW) and a transmission rate of about 1 to 10 megabits.

With the device according to the invention, the slave modules 3 can bepositioned anywhere along the useful part of the rod 1, and theirlateral location is not critical in so far as their transmitters 4 andreceivers 5 merely have to be located within the lateral coupling zone 8which extends, outside the rod, over at least one centimeterperpendicularly to the longitudinal axis S of the rod 1.

It is possible to envisage doubling the number of slave modules 3communicating with a single master module 2 by means of an optical rod1. For this, a second lateral reflector can be arranged at an angle of90° from the lateral reflector 9 on the optical rod 1. Slave modules 3can then be arranged respectively facing the lateral reflector 9 andfacing the second lateral reflector.

1. Device for optical communication between electronic modulescomprising an optically conducting rod (1), having first and secondends, designed to be optically coupled, by lateral coupling, to lateralelectronic modules (3) arranged laterally along the rod, and comprisinglateral reflecting means (9) arranged over a longitudinal part of theexternal surface of the rod (1) opposite the lateral modules (3), devicecharacterized in that the lateral modules (3) are slave modules designedto communicate with a master module (2) optically coupled, axially, tothe first end of the rod, the rod (1) comprising a useful part equippedwith the lateral reflecting means (9) forming a substantially continuousreflecting zone, the rod, which has a cross-section the surface whereofis greater than 15 mm², and the lateral reflecting means defining acontinuous longitudinal lateral coupling zone (8) along the useful partof the rod so as to enable bi-directional optical coupling of the mastermodule (2) with a lateral module (3) arranged at any location along theuseful part of the rod, the lateral coupling zone (8) extending over atleast one centimeter outside the rod.
 2. Device according to claim 1,characterized in that the lateral reflecting means (9) are formed by aplurality of adjacent notches (12) constituting a reflecting zone in theform of serrated teeth along the useful part of the rod (1).
 3. Deviceaccording to claim 2, characterized in that each notch (12) issymmetric.
 4. Device according to claim 2, characterized in that eachnotch (12) is asymmetric and is bounded by a first oblique face (14),forming a first angle (β₁), with an axis perpendicular to thelongitudinal axis (S) of the rod (1), and a second oblique face (15),closer to the second end of the rod (1) and forming a second angle (β₂),smaller than the first angle (β₁), with the axis perpendicular to thelongitudinal axis (S) of the rod (1).
 5. Device according to claim 4,characterized in that the adjacent notches (12) have a variable pitch(p), decreasing progressively between the first and second ends of therod (1).
 6. Device according to claim 5, characterized in that thelateral reflecting means (9) comprise an internal flat surface (16) atthe bottom of the notches (12), the flat surface having a variable width(1 ₂), decreasing progressively between the first and second ends of therod (1).
 7. Device according to claim 5, characterized in that the firstangle (β₁) decreases progressively between the first and second ends ofthe rod (1).
 8. Device according to claim 2, characterized in that twoadjacent notches (12) are separated by an external flat surface. 9.Device according to claim 1, characterized in that the lateralreflecting means (9) comprise a narrow reflecting strip (17, 18, 19,20).
 10. Device according to claim 9, characterized in that thereflecting strip is a continuous rectangular strip (18).
 11. Deviceaccording to claim 9, characterized in that the reflecting strip is afragmented strip (20), comprising elemental reflecting zones of variablelength arranged longitudinally with preset pitch, the length of theelemental reflecting zones, minimal near to the first end of the rod(1), increasing to a preset maximum value then decreasing up to thesecond end of the rod (1).
 12. Device according to claim 9,characterized in that the reflecting strip is a strip (19) of variablewidth, minimal near to the first end of the rod (1), increasing to apreset maximum value then decreasing up to the second end of the rod.13. Device according to claim 11, characterized in that the maximumvalue is closer to the second end of the rod (1) than to the first endthereof.
 14. Device according to claim 9, characterized in that thereflecting strip (17, 18, 19, 20) is obtained by deposition of amaterial of suitable optical index on the external surface of the rod(1).
 15. Device according to claim 1, characterized in that the rod (1)comprises, at its first end, an end section (10) not equipped with alateral reflecting means.
 16. Device according to claim 1, characterizedin that the rod (1) has a circular cross-section.
 17. Device accordingto claim 1, characterized in that the rod (1) has an ovoidcross-section.
 18. Device according to claim 1, characterized in thatthe rod (1) has a rectangular cross-section, the lateral reflectingmeans (9) being arranged on a first lateral face of the rod and thelateral modules (3) arranged along the rod, facing a lateral faceopposite the first face.
 19. Device according to claim 1, characterizedin that the cross-section of the rod (1) decreases continuously from thefirst end of the rod to the second end thereof.
 20. Device according toclaim 1, characterized in that the second end of the rod (1) comprisesan end reflector (11).
 21. Device according to claim 1, characterized inthat the second end of the rod (1) is inclined (α) with respect to thelongitudinal axis (S) of the rod.
 22. Device according to claim 1,characterized in that the first end of the rod (1) comprises means (21)for flush-mounted housing of electro-optical transmitter (4) andopto-electronic receiver (5) elements of the master module (2). 23.Device according to claim 1, characterized in that the lateral modules(3) are electrical control/monitoring and/or protection units, arrangedin an electrical panel (22).
 24. Device according to claim 23,characterized in that the lateral modules (3) are arranged side by sidealong the useful part of the rod (1).
 25. Device according to claim 24,characterized in that the master module (2) is situated at a locationremote from the electrical panel (22) and optically connected to thefirst end of the rod (1) by an additional optical rod (23) comprising acoupling end for coupling with the first end of the rod (1).
 26. Deviceaccording to claim 25, characterized in that the additional optical rod(23) is arranged perpendicularly to the rod (1), with a coupling endcomprising an external face in contact with the first end of the rod (1)and a reflecting end surface (24) forming an angle of 45° with the firstend of the rod.
 27. Device according to claim 24, characterized in thatthe rod (1) has an elbow at its first end.